On Oct. 10, Leonardo Ureña of Napa won the Half Moon Bay giant pumpkin weigh-off with a 1704-pound behemoth — a new California record. Ureña is part of a blooming subculture of competitive pumpkin growers that are smashing pumpkin records left and right. The world record, set this year at 1818.5 pounds, has been beaten each year for three straight years.

The sport dates back to 1900, when Canadian grower William Warnock grew a 400-pound specimen, declared a world record at the Paris World’s Fair. Since then, record-breaking pumpkins have more than quadrupled in weight. The pumpkin enthusiast website Pumpkinnook.com’s once-exclusive “Club 1000” for pumpkins exceeding 1,000 pounds was updated in 2004 to become the “1100 Club.”

Giant pumpkins on display at the Stanford Shopping Center in Palo Alto. Can you spot the kid? (Photo by Helen Shen)

Jim Borchard Sr. of Borchard Farms in Salinas believes that much of this explosive growth can be traced to genetics. He’s been growing giant pumpkins for over 30 years and even won the Half Moon Bay contest several times “before the pumpkins started getting really big.”

According to Borchard, about 15 years ago, many growers started making super-giant varieties by cross-pollinating pumpkin plants by hand—using a cotton swab to transfer pollen from the male flower of one giant pumpkin to the female flower of another giant pumpkin.

Normally, each pumpkin plant grows several fruits on the same vine. Most modern competitive growers pinch off all the stems but one so that the nutrients from the roots are funneled to a single pumpkin. That one pumpkin could yield anywhere from a few hundred to a thousand seeds. Borchard belongs to the close-knit community of giant pumpkin growers who connect over the internet and swap their best seeds at seed meetings.

If all these pumpkin growers are tapping the same gene pool, I had to wonder whether winning one of these contests comes down to sheer luck. Borchard says luck certainly plays a part. Pumpkin splitting, which happens in normal pumpkins, too, occurs at devastatingly high rates in the giants. Depending on weather and geography, growers need to feed each plant about 500 gallons of water per week. “In August, these guys are taking on sometimes 40 pounds in one day,” he said, and the skin doesn’t always keep pace with the expansion.

Joel Holland holds the Washington state record with this pumpkin from 2009. (Photo by Mari Lou Holland)

Weather is another unpredictable factor. Joel Holland, a giant pumpkin grower from Sumner, Wash., says pumpkins typically fare better at northerly latitudes, but in the last 10 years, he’s seen the epicenter of winning pumpkins shift farther south. He’s noticed a general cooling trend that has helped produce ideal growing conditions in California, while making his own state a little too cold.

Bad weather and pumpkin explosions aside, serious growers can and do try to control other factors. Holland runs a thriving business that sells supplies, fertilizers, and instructional DVDs to fellow giant pumpkin growers.

One of his most popular products is a mycorrhizal soil treatment, which infects the pumpkin root system with a sort of helper fungus. The fungus lives inside the root and puts out “hyphae,” which are tiny rootlets that scout out valuable phosphorus in the soil and bring it back to the mothership. In exchange, the fungus feeds off sugars in the roots.

The contests are decided by weight, not size — although the two are usually correlated. When Holland trucked his own world record-breaking pumpkin from Washington to the Half Moon Bay festival in 1992, he took precautions to keep the fruit from losing water weight through its surface (a process called transpiration). Soaking the stem in water and filling his pickup truck bed with ice helped keep the pumpkin cool and hydrated on the three-day road trip. That pumpkin kept its weight and took first place at 827 pounds.

Is the sky the limit?

So what does one do with a pumpkin the size of a refrigerator? “You’re probably not going to want to make pie out of it,” said Borchard. Most contest pumpkins are not grown for tastiness, and some can have rinds up to 8 to 10 inches thick. Instead, Borchard saves some seeds for trading and planting, and uses the remaining pumpkin bits to feed his cattle and sheep through the winter. Many giant pumpkins are also purchased by businesses for holiday displays.

If there’s any limit to the size these pumpkins can reach, recent data suggests we may still be a ways off. My own data crunching revealed an approximately linear increase in world record pumpkin weights over the past three decades.

“People used to talk like we wouldn’t ever break 1,000,” said Holland. “I’m sure there will be a 1-ton pumpkin within the next 10 years.”